This invention relates to a dual thermostat control apparatus for conditioning and maintaining environmental air in a predetermined condition.
The air supplied to a building or other enclosure is conventionally treated by a heating, ventilating and air conditioning system to create and maintain the air in a predetermined desired condition including a selected temperature. Normally, one or more thermostatic devices are mounted within the enclosed area or space to sense the temperature condition and to generate corresponding related demand signals. Various electrical and pneumatic thermostatic devices are commercially available to create the appropriate signal for connection as the input to a control system. A dual thermostatic unit may be provided to create a dual output, one of which controls a heat source for heating the air supplied to the conditioned space and a second of which controls a cooling source for cooling of the air to be supplied to the conditioned space. For example, U.S. Pat. No. 3,140,047 discloses a dual thermostatic device having a multiple supply pressure selector for changing over from a heating to a cooling condition. A pair of separate bimetal-leak port assemblies are provided to separately control the heating and the cooling. A duplex relay couples thermostatic fluid signals as the temperature related signals into the common control for operating a heating unit during the heating seasons and alternatively operating of a cooling unit during the air cooling seasons. A manual selector switch couples the proper supply to the thermostatic unit and provides for automatic actuation and setting of the relay system to respond to the appropriate heating or cooling thermostat. Although such a device provides an effective control, it does not provide an automatic switch-over condition nor does it provide for an interrelated limit control on the heating and cooling of the conditioned air to be supplied to the enclosed space. Other dual thermostat devices are shown, for example, in U.S. Pat. Nos. 3,115,039 and 3,166,085.
In various installations, the operator may desired, or may be required, to establish a predetermined maximum heated condition and a maximum cold or cooled condition in the conditioned space. The maximum condition may be the same or may provide a predetermined range over which heating and cooling may occur. Thus, a range would be created over which neither heating or cooling energy is supplied with a resulting energy conservation. The greater the non-operative or dead band range the greater the savings which will be obtained. For example, in an office environment, an apartment environment or the like, a set point temperature of 73.degree. may be selected. If the system may be set to permit heating of the environmental space to some level below 73.degree. and cooling to some level above 73.degree. the necessary comfort condition may be provided at a minimal energy cost. This temperature differential or dead band region thus decreases the total energy consumption. The control system may practically allow fluctuation of the temperature within a total range of 13.degree., or 61/2.degree. to either side of the set point temperature. The control system would then become operative in the control range of approximately 65.degree. to 78.degree.. Such a system may be particularly useful in certain areas as a result of governmental standards which dictate a maximum temperature condition during the heating season and minimum temperatures in the cooling seasons in certain public or other multiple unit buildings. Further, it may be desirable to vary the dead band temperature at which heating terminates below the maximum level during night time hours as related to daytime hours. Similarly, it may be desired to adjust the upper cooling limit during certain times of the day.
Although various dual thermostatic devices are available, the controls generally permit crossover within any given range and do not have predetermined limit settings above which heating will not occur and below which cooling will not occur. Although sophisticated computer based controls for large building installations may permit corresponding sophisticated control including temperature limits, such systems are not economically significant for smaller installations and for individual control and selection.
There is therefore a significant need for a suitable automatic thermostatic control apparatus for adjusting heating and cooling equipment in accordance with the condition of the air within the conditioned space while limiting the heating and cooling equipment operation to establish predetermined maximum temperature limits during heating and cooling, and for optimum control permitting some adjustment of the range with respect to such conditions.